The large masseter muscle (masseteric hypertrophy), unlike the prominent bony jaw angle, does not have a surgical solution. Surgical muscular reduction is associated with a high rate of complications and potental disability. As a result, the use of botulinum toxin type A injections (most commonly Botox) has become the standard of treatment to improve lower facial contour due to large masseter muscles.
There is little question that Botox into the masseter muscles can be effective but there is little standardization in dose and injection points of treatment. Dosage amounts vary amongst practitioners as well as treatment schedules. Long-term outcomes of a sustained effect remain wanting.
In the August 2014 issue of Plastic and Reconstructive Surgery, a paper on this topic was published entitled ‘Classification of Masseter Hypertrophy for Tailored Botulinum Toxin Type A Treatment’. In this paper over 500 masseter muscles were classified into bulging types with three degrees of thickness. Over 200 patients were treated with Botox injections of 20 to 40 units per side with one to three injection sites per muscle. After injection, masseter muscle thickness decreased by an average of roughly 33% (13mms to 9mms approximately) as measured three months later. There was a corresponding improvement in the width of the lower face to the upper facial intercanthal distance. Overall patient satisfaction was 96% without any serious complications.
This study provides evidence in a large series of patients that an injectable approach to massteric muscle reduction is effective. Its maximum effect occurs by three months after treatment with a visible reduction is lower facial width. Dosages in units should be increased based on the muscle characteristics anywhere from 20 to 40 units per side. It is important to keep the injections into the bulk of the muscle closer to the jaw angle area to avoid a temporary weakening effect on the buccal branches of the facial nerve.
What this study does not address is how long this muscular facial thinning effect lasts and how many treatments it takes to achieve its maximal effects. It is still unclear as to whether Botox causes a permanent muscle atrophic result in the muscles of mastication.
Dr. Barry Eppley